55.2-59 57 GMC 100 vs 57 Chevy Question?

[Curt - TN]

Hello, I am new to the forum and I am getting ready to start two truck projects. One for my wife is a 1950 5 window and the one I have questions about is a 1957 GMC 100 that I am getting from a family member.

Is the GMC and Chevy basically the same body and chassis or are they different? I notice the GMC has 6 lug wheels, not sure if the 57 Chevy has 6 lug or not.

I have plans of doing a Heidts Mustang II on the front, shortening the truck down to a short bed, installing an LS, auto and a 4 link rear. I may swap the rear end out because the IFS is 5 log and I would like the back to be 5 lug too.

I called Heidts and talked to them and they seem to think the GMC chassis is more like a 3/4 ton if it has the 6 lug wheels and they say the standard Chevy IFS will not work. They did say if I send them measurements they can find something that will work.

The truck looks rough but it is a California truck so rust should be minimal. I will not be able to get it transported for 3 or 4 weeks so I have only seen pictures.

Thanks,

[Foot Stomper]

Welcome to the forum and congratulations on your first post!

The GMC is not a 3/4 ton. 6 lug is how 57's and other years were built...both Chevy and GMC. The "100" tells us this.

The differences are motor and trim design for the most so far as I know but know they can be (and are) different in many ways that you'd never suspect. Just don't assume they are the same because the General made them.

Good luck with your project! Post lots of pictures as you build...we like pictures.

[Kim57]

Welcome.
Sorry I can't give any info on the differences between the two other than the dash layout.
Kim

[dubds10]

Front ends are different of course and dash is different. Our '57 GMC has a Heidts Superride and I don't think there's any difference from the Chevy.

[Curt - TN]

Originally Posted by dubds10

Front ends are different of course and dash is different. Our '57 GMC has a Heidts Superride and I don't think there's any difference from the Chevy.

That truck looks sweet, what size tires and wheels do you have on that truck? Did you have to tub the inner bed?

[dsraven]

the chev and gmc frames are the same as long as they would both be 1/2 tons that you are comparing. the biggest difference is the dash and the grille areas. the front fenders have a dimple in them to accept the gmc mustache grill wrap around part so that would be one thing to watch for if you need to swap out a fender or something. the mustache covers the hole where the chevy marker light would be. the gmc has a hole in the hood out front where the emblem goes in. the grilles are obviously different, otherwise the cabs, boxes, frames etc would interchange. just a note on the front end swap, a lot of guys will set the axle centreline ahead of the stock axle centreline because with the sweeping angle at the rear of the front fender wheel opening the wheel looks like it is stuffed into the rear of the fender when you lower the truck. if you stay with a stock height that wouldn't be a concern. i think I set mine an inch ahead, maybe an inch and half. also, there are bolt in kits available now as well so a lot less hassle figuring out angles etc and then welding it all in hoping it is correct.make sure to talk to the tech dept about support and get a detailed instruction on how to install and get angles and measurements etc. I got my kit from TCI and had many problems because (little did I know) they actually had a mix up and shipped the wrong crossmember to me. I made it work but the tech dept was basically no help and I just researched the net till I found specs for a mustangII and then applied that to my set up. plan on purchasing a digital level and laser. the level so you can get accurate details instead of eyeballing a glass bubble builders level and the laser so you can get the frame nice and straight before you start.
good luck, keep us posted with pics of what you are up to.

[dubds10]

Originally Posted by Curt - TN

That truck looks sweet, what size tires and wheels do you have on that truck? Did you have to tub the inner bed?

Thanks, it's on a 20/22 combo. Forget tire size though. Heidts superride with coil overs & a '68 Camaro posi on lowering leafs out back. Not tunbed, it's a tight fit lol Plan is to airbag it & then I'll tub the rear a few inches.

[_Ogre]

all questions answered above... 3/4 and 1 ton trucks had 8 lugs
your gmc 100 was available in 2 wheelbases 114'' and 125.25'', same as chevys; 115'' is 3100 and 125.25'' is 3200

imo... leave the long bed, they are getting more popular as everyone has a short stepside

[Nut Case]

Curt. I'm building a 57 GMC. The only difference is the front Grill, Hood and the dash board sheet metal. I'm using a Flat out (96 C-4 both front and rear) IFS it fits both GMC and Chevy's. There is a difference in the 55 & 56 vs 57's front fenders and hoods. Best of Luck Nut Case

[ChuckDriver]

The Chevy and GMC frames ARE different up front. The engine cross members are a different design in that the GMC core/rad support bolts to it, but the Chevy has separate mounts for the core/rad support on the frame rails. See the attached pic's!

[SideStepper]

ChuckDriver good catch on the frame differences!
To add to that, the GMC radiators & core supports are larger by far on the GMC's than on the Chevys. The GMC's actually had 2 different size radiators, a heavy duty one for the 6 cylinders & huge a radiator on the V-8's.
GMC ran Pontiac engines, not Chevys engines!

[Foot Stomper]

Originally Posted by SideStepper

ChuckDriver good catch on the frame differences!
GMC ran Pontiac engines, not Chevys engines!

And for giggles, the Canadian built GMC 6 cylinder trucks ran the Chevy motor. Isn't this fun?

[dsraven]

one other thing I have noticed is that some have a full width rad support, like mine and chevies do, and some have a u shaped rad support like an AD truck would have. I have only seen pics of that but wonder if that has something to do with the different cross member like it does on the AD trucks between chev and gmc back then. sorry don't have a pic of my rad support but it looks just like a 57 chevy truck rad support. my truck came with a 6 cyl 3 spd.

[dsraven]

chuckdriver, post 10 top pic is what my rad supports looked like on the 57. the 58 frame had the same thing but further forward and the frame was longer out front by a couple inches.

[Curt - TN]

Thanks for the pics!

[dsraven]

here is a pic of what my donor 58 frame looked like out front. the rad support brackets were already unbolted, sorry. the 57 engine crossmember looked the same, by memory, as the 58 did. the 57 rad support held the fenders and the rad bolted to the back side of it.

[1project2many]

There may be a difference in the area near the steering box also. The frame is rolled up so to speak and the distance between lower inside of "C" and upper portion along with distance from outer vertical surface to fold may be different. When a truck was equipped with power steering, Chevrolet used a piston and a drag link mounted control valve where GMC used an actual power steering box which was larger than the manual box. I once bought a '57 GMC Cameo for parts and the factory power steering box did not fit in my '58 Chevrolet frame properly.

[dsraven]

finally found a pic of the 57 rad support for you. all this is sitting on a 58 frame so you can see how much longer the frame is. notice the bolt holes in the frame in front of the rad support mounting bracket that were used for the 58 rad support.the 57 rad support sits that much further back.

[Old57]

Here are some pictures of all of my 57 GMC grill and core support parts to show the difference in the Chevy parts. I'm changing mine to the 55-56 Chevy front end, so I'm getting real familiar with the differences.

[dsraven]

my truck is a Canadian model, maybe why the rad support is different? I have seen pics of others the same though. maybe a midyear change? maybe the reason for 2 different cross members as well?

[Old57]

Originally Posted by dsraven

my truck is a Canadian model, maybe why the rad support is different? I have seen pics of others the same though. maybe a midyear change? maybe the reason for 2 different cross members as well?

Yes, from what I've read, the Canadian trucks had the Chevy core support.

[dsraven]

you know, its been awhile since I took my truck apart. I honestly don't remember what holds the front fenders apart behind the bumper. same as chevy trucks with the same rad support I suppose. will have to do a search through my stuff and see if anything looks like it fits there, haha.
nice pics old57. I wish they were like mine so I would know what to look for inmy pile of parts.

[Old57]

I'm converting my 57 GMC to the 55-56 Chevy, so all of these parts in the picture will be changed out for the Chevy stuff.

[roger55]

Btw,
There were 3 different length stepside trucks and yours is the longest one at 97".
From what I've seen, that is the most rare of the 3.
It's only the second 97" bed truck with a big back window I've seen.

I second the opinion to leave your truck with the long bed. But, make yourself happy.

[Strider]

Originally Posted by dsraven

my truck is a Canadian model, maybe why the rad support is different? I have seen pics of others the same though. maybe a midyear change? maybe the reason for 2 different cross members as well?

Does any none have a diagram or a reference to a book or something that shows how a 57 GMC grill goes together? I have all the parts - just trying to Jedi mind trick them together. And this is the CANADIAN version with the Chevy rad support.

Anything, anyone! It came in pieces and I lost the lego instruction sheet!